1. Field of the Invention
The present invention relates to the use of lasers to remove unwanted sub-surface tissue from a living being, such as a human. More particularly, the invention concerns a method for selectively destroying relatively deep sub-epidermal formations of unwanted tissue by heating water in the formations with a laser. This causes protein denaturing such as spatial protein conformation, without excessively damaging the unwanted tissue.
2. Description of the Related Art
In the field of cosmetic surgery, one important concern is the treatment of highly vascularized tissues, such as capillary blood vessels, strawberry hemangiomas, spider veins, telangiectasia, and the like. In this respect, many known techniques are aimed at eliminating or reducing such tissue. Some of these techniques, for example, include surgical dissection, sclerotherapy, and electro-cuttering. With surgical dissection, the patient is first anesthetized and then a cutting device such as a scalpel is used to surgically remove the vascularized tissue. With sclerotherapy, an alcohol-based substance is injected into veins for clotting of the veins. With electro-cuttering, a high-voltage scalpel is used to effectively "cut out" the unwanted tissue while coagulating blood in the region. Usually, healing of the treated tissue occurs after formation of a lesion on the skin's surface at the treatment site.
Although these techniques may be satisfactory in some applications, they may prove inadequate in certain other circumstances. For instance, certain patients may object to the pain caused by these procedures. Additionally, some patients may experience excessive bleeding, internally and/or externally. Furthermore, these procedures may inflame the treated tissue in some cases, and lead to healing by second tension. Another potential drawback of known methods concerns the post-treatment healing time, which some may find excessive. Further, in certain cases these techniques have been known to leave scars or other noticeable marks. Although sclerotherapy may be effective for treating big veins, some may complain that sclerotherapy is not sufficiently effective for smaller vessels such as capillary blood vessels.
In contrast to the techniques described above, some physicians have employed lasers to remove vascularized tissue. In particular, Dye lasers have been used to remove such tissue by destroying blood vessels. In particular, the Dye laser process works by exploding red blood cells and consequently erupting blood vessels. The Dye laser produces wavelengths that have little water absorption and therefore generates relatively deep tissue penetration. On the other hand, the Dye laser produces wavelengths that have a substantial level of oxyhemoglobin absorption. As a result, the Dye laser causes hemoglobin in the erythrocytes to be exploded, causing blood vessel eruption. For some patients, this process may not be satisfactory. In particular, with small formations such as spider veins and telangiectasia, this approach typically provides only a short term cosmetic correction of the tissue. Moreover, even after extended periods of convalescence, many of these patients still experience significant scarring.
In contrast to the Dye laser approach, some physicians have used infrared lasers at 1.9 .mu.m and greater, such as Tm:YAG, Ho:YAG, Er:YSGG, Er:YAG, CO, and CO.sub.2. These techniques often do not enjoy optimum results because of certain operating characteristics of the lasers. Chiefly, the laser is absorbed too readily by water in the patient's tissue, resulting in very poor penetration (e.g., 40-60 .mu.m) of the laser into the patient's tissue. As a result, significant damage occurs to skin surface overlying the tissue region of interest. A need therefore exists for a more effective, less destructive, long term method of destroying unwanted vascular tissue.